The present invention relates generally to a control apparatus for controlling a system of an automotive vehicle in response to sensed dynamic behavior, and more specifically, to a method and apparatus for compensating the system for a misalignment in the sensors of the system.
Dynamic control systems for automotive vehicles have recently begun to be offered on various products. Dynamic control systems typically control the yaw of the vehicle by controlling the braking effort at the various wheels of the vehicle. Yaw stability control systems typically compare the desired direction of the vehicle based upon the steering wheel angle and the direction of travel. By regulating the amount of braking at each corner of the vehicle, the desired direction of travel may be maintained. Typically, the dynamic control systems do not address roll of the vehicle. For high profile vehicles in particular, it would be desirable to control the rollover characteristic of the vehicle to maintain the vehicle position with respect to the road. That is, it is desirable to maintain contact of each of the four tires of the vehicle on the road.
In vehicle roll stability control, it is desired to alter the vehicle attitude such that its motion along the roll direction is prevented from achieving a predetermined limit (rollover limit) with the aid of the actuation from the available active systems such as controllable brake system, steering system and suspension system. Although the vehicle attitude is well defined, direct measurement is usually impossible.
In the vehicle dynamics control systems described above, i.e., yaw and/or roll stability control, the vehicle motion states are controlled through electronically-controlled actuators. The vehicle motion states are usually defined using the vehicle body-fixed frame, called body frame. The three axes of the body frame are defined as x, y and z, where x axis is along the longitudinal forward direction of the vehicle, y axis is along the vehicle lateral direction point to the driver side and z axis is along the vertical direction of the vehicle.
In order to measure or estimate the vehicle motion states defined along the body-axes (x,y,z), motion sensors are used. For example, many systems include an integrated six sensor module set that has three gyro angular rate sensors and three linear acceleration sensors integrated into a single module. The three gyro rate sensors are intended to measure the angular rate of a vehicle about the longitudinal axis of the vehicle (roll rate, denoted as xcfx89x), the angular rate about the lateral axis of the vehicle (pitch rate denoted as xcfx89y) and the angular rate about the vertical axis of the vehicle (yaw rate denoted as xcfx89z). The three acceleration sensors are intended to measure the accelerations along the longitudinal direction of the vehicle (denoted as xcex1x), along the lateral direction of the vehicle (denoted as xcex1y), and along the vertical direction of the vehicle (denoted as xcex1z).
The six sensor outputs might not reflect the real vehicle motion states, which are defined along the vehicle body axes. This happens when the sensor directions of the sensor system do not coincide with the vehicle body axes (x,y,z). This may occur due to sensor mounting errors during insertion of the sensor system during manufacturing.
Other potential error sources for the aforementioned sensor systems exist, including the vibration-induced sensor errors described in WO 01/11318, steady state bias, and the thermal drift described in U.S. Pat. No. 5,527,003. Although those sensor errors can be compensated by using averaging and by learning the sensor bias, the sensor misalignments need to be treated differently. Since the misalignments generate sensor errors that are proportional to the magnitudes of the actual signals, the sensor error is very dynamic, unlike the errors caused by thermal drift and steady state bias.
Partial sensor misalignment has been studied for inertial navigation systems in U.S. Pat. No. 5,789,671 and U.S. Pat. No. 6,081,230, for a forward-looking vehicle sensor in U.S. Pat. No. 5,964,822, and for a vehicle clearance sensor in U.S. Pat. No. 6,026,353. None, however, describe compensation for a sensor system used for a dynamic control system such as a yaw stability control system or a roll stability control system.
It is therefore desirable to detect the amount of errors in the sensor outputs due to sensor misalignments and compensate the various measurements therefore.
The present invention is directed to the roll, pitch and yaw misalignments xcex94xcex8x, xcex94xcex8y and xcex94xcex8z, and compensating the sensor outputs using those detected misalignment angles xcex94xcex8x, xcex94xcex8y and xcex94xcex8z. In this disclosure, the sensor misalignments xcex94xcex8x, xcex94xcex8y and xcex94xcex8z are detected based on the sensor outputs and the computable vehicle motion states, through several sets of relationships between the sensor measurements and the vehicle motion variables.
In one aspect of the invention, a control system for an automotive vehicle having a vehicle body includes a sensor system having a housing oriented within the vehicle body, a roll angular rate sensor positioned within the housing generating a roll angular rate signal corresponding to a roll angular motion of the sensor housing, a yaw angular rate sensor positioned within the housing generating a yaw rate signal corresponding to a yaw motion of the sensor housing, a pitch angular rate sensor positioned within the housing generating a pitch rate signal corresponding to a pitch motion of the sensor housing, a lateral acceleration sensor positioned within the housing generating a lateral acceleration signal corresponding to a lateral acceleration of the sensor housing, a longitudinal acceleration sensor positioned within the housing generating a longitudinal acceleration signal corresponding to the longitudinal acceleration of the sensor housing, and a vertical acceleration sensor positioned within the housing generating a vertical acceleration signal corresponding to the vertical acceleration of the sensor housing. The vehicle also has a safety system such as an airbag, an active braking system, and active steering system, or an active suspension system. A controller is coupled to the roll angular rate sensor, the yaw angular rate sensor, the pitch angular rate sensor, the lateral acceleration sensor, the longitudinal acceleration sensor, and the vertical acceleration sensor. The controller determines a roll misalignment angle, a pitch misalignment angle and a yaw misalignment angle as a function of the sensor outputs of the roll rate, the pitch rate, the yaw rate, the lateral acceleration, the longitudinal acceleration and the vertical acceleration. The controller generates a control signal for controlling the safety system in response to the roll misalignment angle, the pitch misalignment angle and the yaw misalignment angle and the other calculated and measured variables.
In a further aspect of the invention, a method for controlling a vehicle dynamics control system comprises: determining a roll misalignment angle; determining a pitch misalignment angle; determining a yaw misalignment angle; determining the longitudinal acceleration along the vehicle body fixed x-axis by projecting the longitudinal, lateral and vertical acceleration sensor outputs along the body-fixed x-axis in response to said roll misalignment angle, said pitch misalignment angle and the yaw misalignment angle; determining the lateral acceleration along the vehicle body fixed y-axis by projecting the longitudinal, lateral and vertical acceleration sensor outputs along the body-fixed y-axis in response to said roll misalignment angle, said pitch misalignment angle and the yaw misalignment angle; determining the vertical acceleration along the vehicle body fixed z-axis by projecting the longitudinal, lateral and vertical acceleration sensor outputs along the body-fixed z-axis in response to said roll misalignment angle, said pitch misalignment angle and the yaw misalignment angle; determining the roll rate along the vehicle body fixed x-axis by projecting the roll rate, pitch rate, and yaw rate sensor outputs along the body-fixed x-axis in response to said roll misalignment angle, said pitch misalignment angle and the yaw misalignment angle; determining the pitch rate along the vehicle body fixed y-axis by projecting the roll rate, pitch rate, and yaw rate sensor outputs along the body-fixed y-axis in response to said roll misalignment angle, said pitch misalignment angle and the yaw misalignment angle; determining the yaw rate along the vehicle body fixed z-axis by projecting the roll rate, pitch rate, and yaw rate sensor outputs along the body-fixed z-axis in response to said roll misalignment angle, said pitch misalignment angle and the yaw misalignment angle; and activating a safety system as a function of said compensated longitudinal acceleration, lateral acceleration, vertical acceleration, roll rate, pitch rate and yaw together with the other calculated and measured signals.
Other advantages and features of the present invention will become apparent when viewed in light of the detailed description of the preferred embodiment when taken in conjunction with the attached drawings and appended claims.